Test switches are electrical circuit components typically used to simplify the use and replacement of test equipment in electrical power distribution networks, or maintenance of such test equipment, and may be mounted on switchboard panels or interconnection boxes. Test or measuring equipment, including meters and non-drawout relays, may be connected to a first set of terminals of the test switch, and the power distribution network's electrical equipment may be connected to a second set of terminals. When the switch is closed, the test equipment is connected to the power distribution electrical equipment; when the switch is opened, the test equipment is disconnected from the network and may be easily replaced as needed.
Test switches are typically available in single- or multiple-poles units. Each pole consists of a single throw knife blade type switch mounted on a moulded base having pole-isolating barriers which prevent accidental short circuiting between poles. This reduces the possibility of an operator coming in contact with live parts. Moulded Bakelite handles can be provided for either individual or group operation of the poles. When mounted on a switchboard panel for facilitating the testing and changing of meters and non-drawout relays, each stud on a relay or meter is connected to one pole of the test switch. Studs that are terminals of current coils are connected to current poles which have short-circuiting posts that automatically short-circuit the current transformer secondaries when the test switch is opened. When mounted on interconnection boxes to open the control circuits for safety maintenance of equipment, each wire is connected to one pole of the test switch. Wires that are terminals of auxiliary normally closed contact (type B) are connected to poles which have short-circuiting posts that automatically short-circuit and hold up the right image when the test switch is open.
Test switches may be mounted to other electrical equipment and then transported to a location where the electrical equipment is installed. During transportation, G-forces and vibration may cause the test switch to become more loosely attached, or even to become detached from the electrical equipment, and may further cause structural damage to the test switch. To overcome that problem, service personnel are known to disregard the manufacturer fastener torqueing specifications and may choose to apply a higher than the specified torque to prevent the fasteners from becoming loose again. That attempt to solve a problem may create another one, which is cracking of the body of test switches that were not designed to withstand the additional level of fastener torque, which may require the replacement of the entire unit.
The body of the test switch is made of electrically insulating material, such as Bakelite. It has a generally flat bottom which is mounted against the mounting surface that is also generally flat. However, as a result of manufacturing process variations, the degree of flatness of the bottom surface of body cannot be guaranteed with the result that some units may exhibit a surface that is somewhat concave. That concavity produces a bending stress in the body that is dependent on the degree of torque applied to the fasteners; the higher the torque the higher the degree of stress. At some point, the stress may be high enough to cause the body to crack.
As a result, test switches which address at least some of these issues may be of interest to the industry.